Electronic – Why does this optocoupler circuit work without getting destroyed

I)

1. It doesn't. Whether it's low or high, the resistors act as a pull-up while also providing the needed signal. The current, for a supposed logic low would be \$115\sqrt{2}/940k\Omega = 173 \mu A\$

2. As Some Hardware Guy said, it's floating so the reference is 0V because its supply is mono-alternance and done through a capacitive impedance (reactance) of \$1\mu F\ = 2.65k\Omega \$ (60Hz) or\$ 3.18k\Omega\$ (50Hz).

3. They're there for not actually putting the pin to 160V, your fear at #1.

II)

1. C1 has the mentioned reactance, acting as an "active" resistor, limiting current through Z1.
   1. I couldn't find the 0.5W you're talking about.

The rest:

1. The LED will still have ~2V foreard voltage drop and the maximum current will be: \$ I_{max}=\frac{115\sqrt{2}-2}{100k\Omega} = 1.62mA\$

2. There won't be -120V since its reference will be the IC's supply, therefore the bridge will clamp the voltage.

You're welcome, but you should really try those simple circuits that have proven to be good enough, instead of choosing this.

Well, the quick answer is no. That won't work.

1) Your flyback diodes are pointing the wrong way, and will always be ON, shorting out the power supply. They are also not rated for 1.2 amps.

2) Your optocouplers, while not a bad idea, cannot possibly handle the current required.

3) It's not at all clear what your logic function is, and I suspect you intended U1,U3,U14,U18 and U22 to be PNPs.

Since you're willing to use external logic, and apparently don't entirely trust your Pi to provide only one output active at a time, I would suggest you go whole hog on logic (it will only take one IC) and do something like

^{simulate this circuit – Schematic created using CircuitLab}

D0 to D2 are 3 bits from the Pi, and they form a binary address of the motor you want on. A code of 1 to 5 will select the motor you want, and 0,6,or 7 will result in no motors on.

I've shown the 5 optocoupler inputs as LEDs, and I've only shown one output. The flyback diode should be rated for 2 amps or more. A 1-amp diode such as a 1N5817 will actually work, but whenever a motor is turned off the current through the diode will briefly exceed 1 amp. This is probably OK, but bad practice. MOSFETs are n-type. Almost anything will do, since voltage rating is less than 20 volts, and current is 1.2 amps.